The use of roofing membranes as a waterproofing material on buildings is well known. The typical type of roofing membrane consists of a base sheet of a sheet-like material such as, for example, paper, felt, fabric, synthetic polymer film, woven or non-woven fabric, glass fibers, or metal foil with a bitumen (or asphalt) layer coated on both faces of the base sheet. Mineral granules or powder such as fine gravel, sand, or talcum are embedded in the surface of the bitumen layer in order to suppress the stickiness of the bitumen and also to protect the exposed bitumen layer from ultraviolet light after the bituminous roofing membrane is applied on site. The bottom of the membrane is covered with a layer of asphalt which is embedded with a back surfacing material such as sand to prevent the membrane from sticking to another membrane material during shipping and handling.
The above-described roofing membrane is not without problems, however. For example, the asphalt impregnated product has limited elongation properties which make it tend to buckle or crack upon thermal expansion and contraction. In contrast, modified bitumen roofing membrane has the advantages of having greater elongation and flexibility properties compared to unmodified bitumen roofing membrane materials. Modified bitumen has a much greater elasticity than unmodified bitumen and hence is less susceptible to buckling or cracking when exposed to temperature fluctuations.
Due to the nature of asphalt as a lubricant, however, mixing of polymer and asphalt, especially high concentrations of asphalt, to form modified bitumen is not easy to accomplish. Specifically, the viscosity of a blend of asphalt and polymer, which is dependent on the asphalt to polymer ratio, may not allow for good mixing.
Current production of modified asphaltic systems for use such as, for example, roofing membranes is based on a batch mixing process. Different raw materials such as, for example, asphalt, polymers, fillers, and flame retardants are mixed in separate mixing tanks at elevated temperatures. The mixing of raw materials, for example, polymer with asphalt, may require a high sheer device for blending. As such mixing is time consuming, the mixing can be a bottleneck in the production of membranes. Additionally, quality risks can be associated with the mixing, and the amount of modification is limited by the mixing that can be achieved in a batch mixing process.